The instant invention relates to illuminating means used in electrophotocopying machines and the like, and more particularly to those illuminating systems in which the processed optical image takes the form of a line scan.
One such line scan illuminating system scans an original document to be copied and projects a narrow band of light upon the active surface of an electronic charge coupled device (CCD). The linear form of the receptor surface is exceedingly narrow (typically 13 microns), and consequently the illuminated area of the original document must be illuminated correctly to overlay the active area of the CCD.
The fiber optic illuminator enjoys merits as applied to scanning machines such as those based on CCD electronics, the primary reason being that it is possible to project a narrow, high intensity swath of light derived from a relatively low wattage light source. The light pipe property of the fibers permits the fibers to be grouped at one end to form a disc in the proximity of a light source and the other end to be constrained to form a line equal or slightly exceeding the width of the original document to be copied.
In order to have an efficient fiber optic illuminator, there needs to be incorporated between the linear array of fiber ends and the original document being copied a lens element. The need for a lens element arises because the rays emitted from the fiber ends are divergent and a cylinder lens or condenser must be added to cause these rays to converge upon the plane of the original document being copied, thereby forming the intense swath of light.
A suitable lens for a fiber optic illuminator is one of the Fresnel types, which are fabricated from plastic and formed into a thin strip on which has been formed a series of prism-shaped projections extending lengthwise and parallel to the linear array of the fiber optic illuminator. One such Fresnel lens is manufactured by the Visual Products Division of the 3M Corporation and marketed under the name "3M Lensfilm".
A Fresnel lens mounted parallel to the fiber optic illuminator and located intermediate the illuminator and the document to be copied, and spaced from both, serves as a light concentrator. In such arrangements, there is a need to be able to modify the linearity of the swath of light emitted from the illuminator without disturbing the focal adjustment of the system. The instant invention therefore provides a means of modifying the linearity of the swath of light emitted from the illuminator without disturbing the focal adjustment thereof.